The present invention relates generally to lighting devices and more particularly to an organic light emitting diode.
Organic electroluminescent devices, such as organic light emitting diodes (OLEDs), are currently used for display applications and are planned for use in general lighting applications. An OLED device includes one or more organic light emitting layers disposed between two electrodes, e.g., a cathode and a light transmissive anode, formed on a light transmissive substrate. The organic light emitting layer emits light upon application of a voltage across the anode and cathode. Upon the application of a voltage from a voltage source, electrons are directly injected into the organic layer from the cathode, and holes are directly injected into the organic layer from the anode. The electrons and the holes travel through the organic layer until they recombine to form excited molecules or excitons. The excited molecules or excitons emit light when they decay.
Prior art light emitting OLED display devices are currently available. One such device is described in U.S. Pat. No. 5,688,551 (the ""551 patent), incorporated herein by reference. An example of a prior art display device 1 is illustrated in FIG. 1, which is a circuit schematic of a device similar to that described in the ""551 patent. The display device 1 contains an array of OLED subpixels 3. Each subpixel 3 emits a particular color, such as red, green and blue. The device 1 contains a plurality of pixels, each of which includes a red, a green and a blue subpixel 3. Thus, the color emitted by each pixel may be tuned by individually controlling the power provided to each subpixel 3, and a particular pixel may be tuned to emit white light.
The device 1 also contains a column driver circuit 5 and a row driver circuit 7, which control the application of power to each subpixel 3. In order to turn on a particular subpixel 13, the column driver circuit 5 must apply power to the third column in which the particular subpixel 13 is located, and the row driver circuit 7 must apply power to the second row in which the particular subpixel 13 is located. Thus, only the one subpixel 13 located in column three, row two emits light when power is applied to the third column and the second row. Therefore, each subpixel in a display device receives an individual power signal and each subpixel in the display device is controlled separately. Furthermore, each subpixel is separately connected to a power source, since each subpixel has a unique row and column address.
However, the present inventor has realized that such prior art OLED arrays, which are suitable for display devices, would suffer from several disadvantages if used for general lighting applications. The independent subpixel control in the display device of FIG. 1 requires complex fabrication processes and complex driver circuits, and is thus expensive to design and manufacture. This renders the display device of FIG. 1 impracticably expensive for lighting applications. The present invention is directed to overcoming or at least reducing the problems set forth above.
In accordance with one aspect of the present invention, there is provided a light emitting device, comprising an array of organic light emitting diodes (OLEDs) emitting a plurality of colors and a layer of scattering media above the light emitting surface of the array.
In accordance with another aspect of the present invention, there is provided a light emitting device, comprising: (a) an array of OLEDs comprising (i) a first set of a plurality of OLEDs electrically connected together to the same power source such that each OLED receives the same power signal at the same time, the first set of OLEDs emit light of a first color, and (ii) a second set of a plurality of-OLEDs electrically connected together to the same power source such that each OLED receives the same power signal at the same time, the second set of OLEDs emit light of a second color different than the first color, and (b) a power controller which provides a first amount of power to the first set of OLEDs and a second amount of power to the second set of OLEDs to obtain a device light output having a desired color.
In accordance with another aspect of the present invention, there is provided a method of generating white light, comprising providing a first power signal having a first magnitude to a first set of plurality of OLEDs, such that the first set of OLEDs emit light of a first color, providing a second power signal having a second magnitude to a second set of plurality of OLEDs, such that the second set of OLEDs emit light of a second color different than the first color, and passing the light of the first color and the second color through a scattering medium to mix the light of the first and second colors such that the mixed light appears white to a human observer.
In accordance with another aspect of the present invention, there is provided a method of making a light emitting device, comprising: forming an array of OLEDs, electrically connecting a first set of OLEDs which emit light of a first color to the same power source, electrically connecting a second set of OLEDs which emit light of a different second color to the same power source, and forming a layer of scattering medium over the array of OLEDs.